Comment on Hawking radiation and trapping horizons
We consider dynamical black hole formation from a collapsing fluid described
by a symmetric and flat FRW metric. Using the Hamilton-Jacobi method the local
Hawking temperature for the formed trapping/apparent horizon is calculated. The
local Hawking temperature depends on the tunneling path, which we take to be
along a null direction $(\Delta s=0)$. We find that the local Hawking
temperature depends directly on the equation of state of the collapsing fluid.
We argue that Hawking radiation by quantum tunnelling from future inner and
future outer trapping horizons is possible. However, only radiation from a
space-like dynamical horizon has a chance to be observed by an external
observer. Some comparison to existing literature is made.